The present invention relates to a soldering iron, in particular relates to such a device which uses a heater made of a thermistor like Barium-titanate group ceramics, which has a positive temperature coefficient of resistance and larger resistance at high temperature. That heater is abbreviated as PTC.
A prior soldering iron is shown in FIG. 1, in which a bit 1A made of copper is surrounded by a heater made of Nichrome 2A. Alternatively, a Nichrome heater 2B is inserted within a bit 1B as shown in FIG. 2. Nichrome has the negative temperature coefficient, that is to say, the electrical resistance of a Nichrome heater is lower at a high temperature.
Accordingly, a prior soldering iron using a Nichrome heater has the disadvantage that an iron is excessively heated. The too high temperature of a soldering iron provides for the deterioration of a Nichrome heater itself, an insulation component, and even the deterioration of a component to be soldered.
In order to prevent over-heating, an operator must sometimes switch off a soldering iron, and then, the working efficiency of an operator is decreased.
Another prior soldering iron has a temperature control system for preventing an over-heating condition, by utilizing a temperature sensor and an automatic switching system. However, that temperature controlled soldering iron has the disadvantage that the structure is complicated, and the manufacturing cost of a soldering iron is high.
Further, when the heat capacity of a component to be soldered is large, or a high temperature is required, a soldering iron must generate much heat, and thus, consumes much power. Further, when a required temperature is low, the bit is easily cooled although the heat capacity of the soldering iron is small. Therefore, when soldering continuously, the bit can become cooled and the soldering performance is deteriorated. And, more over, a prior small soldering iron has the disadvantage that it takes a long time to reach the desirable temperature.